The move results from an October 2 announcement that the giant index fund company is changing index providers for 22 of its index funds: from MSCI to FTSE and the University of Chicago's CRSP.

Berkshire has two different share classes, but MSCI included only the B share and left out the A share. Since Berkshire's total value comprises both share classes, the CRSP index includes both. The additional purchase represents about 0.5 percent of Berkshire shares.